What is a UTR number?
A UTR, or Unique Taxpayer Reference, is a 10-digit number HMRC gives you when you register for Self Assessment or set up a limited company. HMRC uses it to identify your tax record, and you will see it on tax returns and HMRC letters. It is not your National Insurance number.
Figures checked against gov.uk on . General information, not tax advice.
Where you will see your UTR
For an individual or sole trader, gov.uk points to the HMRC personal tax account, the HMRC app, and old tax returns and HMRC letters. For organisations such as companies, partnerships and trusts, previous tax returns and HMRC documents such as notices to file or payment reminders carry it.
It is sometimes called a tax reference, which is why the same ten digits can appear under more than one name on correspondence.
Personal and company UTRs are different
A limited company has its own Corporation Tax UTR. gov.uk says a company can request it online and that HMRC posts it to the business address registered with Companies House. A director who also files Self Assessment, for dividends for example, needs a personal UTR of their own.
Because the two references belong to different taxpayers, one does not substitute for the other when you file.
How you get one
A UTR is created when you register, not requested separately. Registration is covered in its own entry, and gov.uk says the number usually arrives by post around 15 days afterwards.